Photon mass - uncertainty

Yukawa potential leads to an expression for the amplitude of
.
[tex] \frac{4\pi^2\hbar^2}{q^2 + m^2c^2}[/tex]

m = mass of exchange boson.

An experiment was performed scattering high energy neutrinos off electrons. No change in the cross-section was observed as the momentum transfer q increased from small values to 5 GeV/c. If the precision of the cross section measurements was 1%, what can you deduce about the mass of the exchanged boson?

A. The square of the amplitude is proportional to the cross sectional area. Seems I can just look at it like q = 0. and say [tex] 1.01 = 1 / m^2 => m = 0.995 eV/c^2 [/tex] which would agree with the some theories on the upper limit of the photon mass.
This seems too simple too me, am I missing something?